1,093 research outputs found
Iron fluorescence from within the innermost stable orbit of black hole accretion disks
The fluorescent iron Ka line is a powerful observational probe of the inner
regions of black holes accretion disks. Previous studies have assumed that only
material outside the radius of marginal stability can contribute to the
observed line emission. Here, we show that fluorescence by material inside the
radius of marginal stability, which is in the process of spiralling towards the
event horizon, can have a observable influence on the iron line profile and
equivalent width. For concreteness, we consider the case of a geometrically
thin accretion disk, around a Schwarzschild black hole, in which fluorescence
is excited by an X-ray source placed at some height above the disk and on the
axis of the disk. Fully relativistic line profiles are presented for various
source heights and efficiencies. It is found that the extra line flux generally
emerges in the extreme red wing of the iron line, due to the large
gravitational redshift experienced by photons from the region within the radius
of marginal stability. We apply our models to the variable iron line seen in
the ASCA spectrum of the Seyfert nucleus MCG-6-30-15. It is found that the
change in the line profile, equivalent width, and continuum normalization, can
be well explained as being due to a change in the height of the source above
the disk. We discuss the implications of these results for distinguishing
rapidly-rotating black holes from slowly rotating holes using iron line
diagnostics.Comment: 20 pages, LaTeX. Accepted for publication in Astrophysical Journal.
Figures 3 to 7 replaced with corrected versions (previous figures affected by
calculational error). Some changes in the best fitting parameter
A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model
We present a systematic study of GX 339-4 in both its very high and low hard
states from simultaneous observations made with XMM-Newton and RXTE in 2002 and
2004. The X-ray spectra of both these extreme states exhibit strong reflection
signatures, with a broad, skewed Fe-Kalpha line clearly visible above the
continuum. Using a newly developed, self-consistent reflection model which
implicitly includes the blackbody radiation of the disc as well as the effect
of Comptonisation, blurred with a relativistic line function, we were able to
infer the spin parameter of GX 339-4 to be 0.935 +/- 0.01 (statistical) +/-
0.01 (systematic) at 90 per cent confidence. We find that both states are
consistent with an ionised thin accretion disc extending to the innermost
stable circular orbit around the rapidly spinning black hole.Comment: 10 pages, 10 figures, accepted for publication in MNRAS 17/04/0
Broad iron lines in Active Galactic Nuclei
An intrinsically narrow line emitted by an accretion disk around a black hole
appears broadened and skewed as a result of the Doppler effect and
gravitational redshift. The fluorescent iron line in the X-ray band at
6.4-6.9keV is the strongest such line and is seen in the X-ray spectrum of many
active galactic nuclei and, in particular, Seyfert galaxies. It is an important
diagnostic with which to study the geometry and other properties of the
accretion flow very close to the central black hole. The broad iron line
indicates the presence of a standard thin accretion disk in those objects,
often seen at low inclination. The broad iron line has opened up strong
gravitational effects around black holes to observational study with
wide-reaching consequences for both astrophysics and physics.Comment: 26 pages. Invited review, accepted for publication in PAS
Constraining the Spin of the Black Hole in Fairall 9 with Suzaku
We report on the results of spectral fits made to data obtained from a 168
ksec Suzaku observation of the Seyfert-1 galaxy Fairall 9. The source is
clearly detected out to 30 keV. The observed spectrum is fairly simple; it is
well-described by a power-law with a soft excess and disk reflection. A broad
iron line is detected, and easily separated from distinct narrow components
owing to the resolution of the CCDs in the X-ray Imaging Spectrometer (XIS).
The broad line is revealed to be asymmetric, consistent with a disk origin. We
fit the XIS and Hard X-ray Detector (HXD) spectra with relativistically-blurred
disk reflection models. With the assumption that the inner disk extends to the
innermost stable circular orbit, the best-fit model implies a black hole spin
parameter of a = 0.60(7) and excludes extremal values at a high level of
confidence. We discuss this result in the context of Seyfert observations and
models of the cosmic distribution of black hole spin.Comment: Accepted for publication in Ap
On the determination of the spin of the black hole in Cyg X-1 from X-ray reflection spectra
The spin of Cygnus X-1 is measured by fitting reflection models to Suzaku
data covering the energy band 0.9-400 keV. The inner radius of the accretion
disc is found to lie within 2 gravitational radii (r_g=GM/c^2) and a value for
the dimensionless black hole spin is obtained of 0.97^{+0.014}_{-0.02}. This
agrees with recent measurements using the continuum fitting method by Gou et
al. and of the broad iron line by Duro et al. The disc inclination is measured
at 23.7^{+6.7}_{-5.4} deg, which is consistent with the recent optical
measurement of the binary system inclination by Orosz et al of 27+/-0.8 deg. We
pay special attention to the emissivity profile caused by irradiation of the
inner disc by the hard power-law source. The X-ray observations and simulations
show that the index q of that profile deviates from the commonly used,
Newtonian, value of 3 within 3r_g, steepening considerably within 2r_g, as
expected in the strong gravity regime.Comment: 7 pages, 10 figures, MNRAS in pres
Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure
The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. These lines serve as powerful probes for examining
the structure of inner regions of accretion disks. Previous studies of line
emission have considered geometrically thin disks only, where the gas moves
along geodesics in the equatorial plane of a black hole. Here we extend this
work to consider effects on line profiles from finite disk thickness, radial
accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution,
and find that within this framework, turbulent broadening is the dominant new
effect. The most prominent change in the skewed, double-horned line profiles is
a substantial reduction in the maximum flux at both red and blue peaks. The
effect is most pronounced when the inclination angle is large, and when the
accretion rate is high. Thus, the effects discussed here may be important for
future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ;
short results of this paper appeared before as a conference proceedings
(astro-ph/9711214
Extreme Warm Absorber variability in the Seyfert Galaxy Mrk 704
In about half of Seyfert galaxies, the X-ray emission is absorbed by an
optically thin, ionized medium, the so-called "Warm Absorber", whose origin and
location is still a matter of debate. The aims of this paper is to put more
constraints on the warm absorber by studying its variability. We analyzed the
X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three
years apart, by XMM-Newton. The spectra were well fitted with a two zones
absorber, possibly covering only partially the source. The parameters of the
absorbing matter - column density, ionization state, covering factor - changed
significantly between the two observations. Possible explanations for the more
ionized absorber are a torus wind (the source is a polar scattering one) or, in
the partial covering scenario, an accretion disk wind. The less ionized
absorber may be composed of orbiting clouds in the surroundings of the nucleus,
similarly to what already found in other sources, most notably NGC 1365.Comment: 10 pages. Accepted for publication in Astronomy & Astrophysic
The broad iron Kalpha line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode
We present the analysis of the broadened, flourescent iron Kalpha line in
simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The
XMM-Newton data were taken in a modified version of the timing mode of the
EPIC-pn camera. In this mode the lower energy threshold of the instrument is
increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the
source, while at the same time preserving the signal-to-noise ratio in the Fe
Kalpha band. We find that the best-fit spectrum consists of the sum of an
exponentially cut off power-law and relativistically smeared, ionized
reflection. The shape of the broadened Fe Kalpha feature is due to strong
Compton broadening combined with relativistic broadening. Assuming a standard,
thin accretion disk, the black hole is close to rotating maximally.Comment: Astron. Astrophys., in pres
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Usefulness of gene expression profiling of bronchoalveolar lavage cells in acute lung allograft rejection.
BackgroundChronic lung allograft dysfunction (CLAD) is the main limitation to long-term survival after lung transplantation. Because effective therapies are lacking, early identification and mitigation of risk factors is a pragmatic approach to improve outcomes. Acute cellular rejection (ACR) is the most pervasive risk factor for CLAD, but diagnosis requires transbronchial biopsy, which carries risks. We hypothesized that gene expression in the bronchoalveolar lavage (BAL) cell pellet (CP) could replace biopsy and inform on mechanisms of CLAD.MethodsWe performed RNA sequencing on BAL CPs from 219 lung transplant recipients with A-grade ACR (nâŻ=âŻ61), lymphocytic bronchiolitis (nâŻ=âŻ58), infection (nâŻ=âŻ41), or no rejection/infection (nâŻ=âŻ59). Differential gene expression was based on absolute fold difference >2.0 and Benjamini-adjusted p-value â€0.05. We used the Database for Annotation, Visualization and Integrated Discovery Bioinformatics Resource for pathway analyses. For classifier modeling, samples were randomly split into training (nâŻ=âŻ154) and testing sets (nâŻ=âŻ65). A logistic regression model using recursive feature elimination and 5-fold cross-validation was trained to optimize area under the curve (AUC).ResultsDifferential gene expression identified 72 genes. Enriched pathways included T-cell receptor signaling, natural killer cell-mediated cytotoxicity, and cytokine-cytokine receptor interaction. A 4-gene model (AUCâŻ=âŻ0.72) and classification threshold defined in the training set exhibited fair performance in the testing set; accuracy was 76%, specificity 82%, and sensitivity 60%. In addition, classification as ACR was associated with worse CLAD-free survival (hazard ratioâŻ=âŻ2.42; 95% confidence intervalâŻ=âŻ1.29-4.53).ConclusionsBAL CP gene expression during ACR is enriched for immune response pathways and shows promise as a diagnostic tool for ACR, especially ACR that is a precursor of CLAD
Simultaneous EUVE/ASCA/RXTE Observations of NGC 5548
We present simultaneous observations by EUVE, ASCA, and RXTE of the type~1
Seyfert galaxy NGC 5548. These data indicate that variations in the EUV
emission (at keV) appear to lead similar modulations in higher
energy (\ga 1 keV) X-rays by 10--30 ks. This is contrary to popular
models which attribute the correlated variability of the EUV, UV and optical
emission in type~1 Seyferts to reprocessing of higher energy radiation. This
behavior instead suggests that the variability of the optical through EUV
emission is an important driver for the variability of the harder X-rays which
are likely produced by thermal Comptonization. We also investigate the spectral
characteristics of the fluorescent iron K line and Compton reflection
emission. In contrast to prior measurements of these spectral features, we find
that the iron K line has a relatively small equivalent width
(eV) and that the reflection component is consistent
with a covering factor which is significantly less than unity (--0.5). Notably, although the 2--10 keV X-ray flux varies by % and the derived reflection fraction appears to be constant throughout our
observations, the flux in the Fe~K line is also constant. This behavior
is difficult to reconcile in the context of standard Compton reflection models.Comment: 13 pages, 6 figures, LaTeX, uses emulateapj.sty and apjfonts.sty,
submitted to Ap
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